Unformatted text preview: o this. Other approaches are more commonly employed in order to reduce the
cost of the calculations. For example, a small model of the active site may be extracted from a crystal structure and
only that portion treated with quantum mechanics. In that case, as is illustrated in an article by Friesner [R. A.
Friesner and B. D. Dunietz, Acc. Chem. Res. 2001, 34, 351], it is important to test that the extracted portion is
large enough so that when optimized it still appropriately reflects the geometry of the active site.
QM / MM Hybrid Approaches
Another approach to the study of large biomolecular systems is to treat the active site with quantum mechanics and
the rest of the molecule with molecular mechanics. This is called the QM/MM method. It has been applied
successfully to a wide variety of systems. See, for example, articles by Friesner [V. Guallar and R. A. Friesner, J.
Am. Chem. Soc. 2004, 126, 8501] and Jensen [H. Li, A. W. Hains, J. E. Everts, A. D. Robertson, and J. H.
Jensen, J. Phys...
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